Line Numbers: Fixed class name on website

This fixes #2487.

plugins/line-numbers/index.html

@@ -24,7 +24,7 @@ <h1>How to use</h1>
   <p>Obviously, this is supposed to work only for code blocks (<code>&lt;pre>&lt;code></code>) and not for inline code.</p>
   <p>Add the <code>line-numbers</code> class to your desired <code>&lt;pre></code> or any of its ancestors, and the Line Numbers plugin will take care of the rest. To give all code blocks line numbers, add the <code>line-numbers</code> class to the <code>&lt;body></code> of the page. This is part of a general activation mechanism where adding the <code>line-numbers</code> (or <code>no-line-numbers</code>) class to any element will enable (or disable) the Line Numbers plugin for all code blocks in that element. <br> Example:</p>
 
-  <pre><code>&lt;body class="line-number"> &lt;!-- enabled for the whole page -->
+  <pre><code>&lt;body class="line-numbers"> &lt;!-- enabled for the whole page -->
 
 	&lt;!-- with line numbers -->
 	&lt;pre>&lt;code>...&lt;/code>&lt;/pre>
@@ -36,7 +36,7 @@ <h1>How to use</h1>
 		&lt;!-- without line numbers -->
 		&lt;pre>&lt;code>...&lt;/code>&lt;/pre>
 		&lt;!-- enabled for a specific element - with line numbers -->
-		&lt;pre class="line-number">&lt;code>...&lt;/code>&lt;/pre>
+		&lt;pre class="line-numbers">&lt;code>...&lt;/code>&lt;/pre>
 
 	&lt;/div>
 &lt;/body></code></pre>